High speed labeling of containers requires accurate feeding of a web of film material into a cutting mechanism where the web of film is cut into labels which are subsequently applied onto containers. In many labeling apparatus, the web is fed onto a cutting drum where the web aligns with a cut point defined by the drum for cutting the web into labels. The cut labels are then transferred to a label transport drum where the label moves into a container wrapping position to engage a container for wrap around labeling.
During web feeding, it is essential that the web graphics align with predetermined positions along the path of travel so that the web is cut along areas defined by the web graphics to form cut labels. Typically, close control of web feed is maintained by the use of expensive differential transmissions which drive web engaging feed rolls. The position of the cutting drum or label transport drum are known throughout the labeling cycle by encoders operatively connected to a controller. The graphics on the web are sensed during web feeding and the transmissions are adjusted as necessary to ensure web feed cutting so that the labels are cut properly. Expensive servomotors have also been employed for web control in labeling machines.
Both differential transmissions and servomotors are expensive and it would be more desirable to use inexpensive AC induction motors for driving feed rollers. However, the AC induction motors have slower reaction time than servo motors, and therefore, up until the present invention, servomotors were used because of the rapidly changing feed speeds during production. Additionally, the acceleration error in closed loop control systems heretofore made use of even servo motors less than optimum, making the use of AC induction motors even less desirable.